WINAPI How to zoom scale by scrolling?

To implement zoom scaling by scrolling using the Windows API, you can follow these steps:

1. Capture scroll messages: You need to capture the scroll messages (WM_MOUSEWHEEL or WM_MOUSEHWHEEL) in the window procedure of your application. Handle these messages to perform the zoom scaling logic.

2. Adjust the zoom factor: Maintain a zoom factor variable that represents the current zoom level of your application. By default, it can be set to 100% (no zoom). When receiving scroll messages, adjust the zoom factor based on the scrolling direction and increment or decrement it accordingly.

3. Redraw the content: After updating the zoom factor, redraw the content in your window to reflect the new zoom level. You can use the InvalidateRect and UpdateWindow functions to trigger a repaint of the window.

4. Scale the content: When drawing the content, apply the zoom factor to scale the content appropriately. You can use transformation functions like SetWorldTransform or SetWindowExtEx in combination with ScaleViewportExtEx to scale the content during drawing operations.

Here's a code example to demonstrate the basic implementation:

cppCopy code
// Global variable to store the zoom factor

double g_zoomFactor = 1.0;



LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)

{

    switch (uMsg)

    {

        case WM_MOUSEWHEEL:

        case WM_MOUSEHWHEEL:

        {

            // Check the scrolling direction

            int zDelta = GET_WHEEL_DELTA_WPARAM(wParam);

            if (uMsg == WM_MOUSEHWHEEL)

                zDelta = GET_WHEEL_DELTA_WPARAM(wParam) / WHEEL_DELTA;



            // Adjust the zoom factor based on scrolling

            if (zDelta > 0)

                g_zoomFactor += 0.1; // Increase zoom factor

            else if (zDelta < 0)

                g_zoomFactor -= 0.1; // Decrease zoom factor



            // Ensure the zoom factor is within a desired range

            if (g_zoomFactor < 0.1)

                g_zoomFactor = 0.1;

            else if (g_zoomFactor > 2.0)

                g_zoomFactor = 2.0;



            // Redraw the window

            InvalidateRect(hwnd, NULL, TRUE);

            UpdateWindow(hwnd);

            return 0;

        }



        // Handle other messages as needed



        default:

            return DefWindowProc(hwnd, uMsg, wParam, lParam);

    }

}



int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)

{

    // Register window class and create the window



    MSG msg = {};

    while (GetMessage(&msg, NULL, 0, 0))

    {

        TranslateMessage(&msg);

        DispatchMessage(&msg);

    }



    return 0;

}

In this example, the WM_MOUSEWHEEL and WM_MOUSEHWHEEL messages are captured, and the zoom factor is adjusted based on the scrolling direction. The window is then invalidated and repainted to reflect the new zoom level. You'll need to integrate this code into your own Windows application to handle zoom scaling by scrolling according to your specific needs.

Note: This example assumes a basic understanding of the Windows API and message handling in a Win32 application.